Yz125 sputtering in mid range

01buck1/4
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01buck1/4
Edited Date/Time 10/12/2021 5:44pm
Happy 4th all!
I have a question about the ignition on my bike. Its an 01 yz125 all stock. However it has started sputtering at half throttle right before powermand. I tested the stator and that is whithin spec. Reeds are good. Crank seals amd top end are good. Coil is good carb is clean and jetted properly. Plug is brand new. I even disconnected the kill switch. I feel like ive narrowed it down to a bad cdi box but would like a second opinion. Any help is greatly appreciated!
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Blackjack31
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Blackjack31 7/4/2017 3:24pm
7/4/2017 3:24pm
Are you 100% sure that it is jetted properly? Have you jetted it or did you take it somewhere? I know a guy who there CDI box was bad and they actually couldn't tell when they were riding it. He kept burning holes in the top of his piston and that's how he found out. idk much about the electrical parts of a bike but I don't know that you can tell when a CDI box is bad. I would buy one or two leaner main jets and see where that takes you. Like 6$ a piece
01buck1/4
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01buck1/4 7/4/2017 3:41pm
7/4/2017 3:41pm
Blackjack31 wrote:
Are you 100% sure that it is jetted properly? Have you jetted it or did you take it somewhere? I know a guy who there CDI...
Are you 100% sure that it is jetted properly? Have you jetted it or did you take it somewhere? I know a guy who there CDI box was bad and they actually couldn't tell when they were riding it. He kept burning holes in the top of his piston and that's how he found out. idk much about the electrical parts of a bike but I don't know that you can tell when a CDI box is bad. I would buy one or two leaner main jets and see where that takes you. Like 6$ a piece
Positive. I have been running this jetting for about 2 years now with no problems at all and ive always made sure the carb was spotless also
Blackjack31
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Blackjack31 7/4/2017 4:03pm
7/4/2017 4:03pm
Blackjack31 wrote:
Are you 100% sure that it is jetted properly? Have you jetted it or did you take it somewhere? I know a guy who there CDI...
Are you 100% sure that it is jetted properly? Have you jetted it or did you take it somewhere? I know a guy who there CDI box was bad and they actually couldn't tell when they were riding it. He kept burning holes in the top of his piston and that's how he found out. idk much about the electrical parts of a bike but I don't know that you can tell when a CDI box is bad. I would buy one or two leaner main jets and see where that takes you. Like 6$ a piece
01buck1/4 wrote:
Positive. I have been running this jetting for about 2 years now with no problems at all and ive always made sure the carb was spotless...
Positive. I have been running this jetting for about 2 years now with no problems at all and ive always made sure the carb was spotless also
Yeah but jetting will change within a month and that's usual. I've seen it change within the day. I would double check on jets. But as far as the CDI box, I would rule that out. I'm not mechanic but I have seen a lot of crazy stuff and the CDI problem I seen didn't have these symptoms. Usually a CDI box will make a bike run really hot. So if the piston is not in bad shape I would say no on the CDI box
01buck1/4
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01buck1/4 7/4/2017 4:13pm
7/4/2017 4:13pm
Blackjack31 wrote:
Are you 100% sure that it is jetted properly? Have you jetted it or did you take it somewhere? I know a guy who there CDI...
Are you 100% sure that it is jetted properly? Have you jetted it or did you take it somewhere? I know a guy who there CDI box was bad and they actually couldn't tell when they were riding it. He kept burning holes in the top of his piston and that's how he found out. idk much about the electrical parts of a bike but I don't know that you can tell when a CDI box is bad. I would buy one or two leaner main jets and see where that takes you. Like 6$ a piece
01buck1/4 wrote:
Positive. I have been running this jetting for about 2 years now with no problems at all and ive always made sure the carb was spotless...
Positive. I have been running this jetting for about 2 years now with no problems at all and ive always made sure the carb was spotless also
Blackjack31 wrote:
Yeah but jetting will change within a month and that's usual. I've seen it change within the day. I would double check on jets. But as...
Yeah but jetting will change within a month and that's usual. I've seen it change within the day. I would double check on jets. But as far as the CDI box, I would rule that out. I'm not mechanic but I have seen a lot of crazy stuff and the CDI problem I seen didn't have these symptoms. Usually a CDI box will make a bike run really hot. So if the piston is not in bad shape I would say no on the CDI box
Awesome thanks man ill double check that needle too and then go from there

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Blackjack31
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Blackjack31 7/5/2017 7:01am
7/5/2017 7:01am
01buck1/4 wrote:
Awesome thanks man ill double check that needle too and then go from there
Good luck to you man!
Paw Paw
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Paw Paw 7/5/2017 9:17am
7/5/2017 9:17am
Look for wear spots or flat spots on the needle and needle jet as they do wear.

Paw Paw
Falcon
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Falcon 7/5/2017 1:42pm
7/5/2017 1:42pm
Also, I hate to follow up on the obvious since you seem to know as much as I do (or more,) but is the gasoline new?
01buck1/4
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01buck1/4 7/5/2017 1:55pm
7/5/2017 1:55pm
Falcon wrote:
Also, I hate to follow up on the obvious since you seem to know as much as I do (or more,) but is the gasoline new?
I definately know alot but am just stumped on this haha and yeah brand new fuel and oil lol
01buck1/4
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01buck1/4 7/5/2017 1:58pm
7/5/2017 1:58pm
Paw Paw wrote:
Look for wear spots or flat spots on the needle and needle jet as they do wear.

Paw Paw
By needle jet do you mean by main jet holder? Thats all i can find on the shop manual
Paw Paw
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Paw Paw 7/5/2017 3:21pm
7/5/2017 3:21pm
The tube that holds the main jet is also the needle jet.

Paw Paw
01buck1/4
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01buck1/4 7/5/2017 7:07pm
7/5/2017 7:07pm
Upon further inspectionidk how this got by me i found this on my reed cage after pulling off the reeds. Looks very deteriorated. Would this be a cause of it by chance?

Paw Paw
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Paw Paw 7/6/2017 11:28am
7/6/2017 11:28am Edited Date/Time 7/6/2017 11:29am
YES, that will keep the reeds from sealing. I have seen that when race fuel is in use.

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01buck1/4
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01buck1/4 7/6/2017 12:22pm
7/6/2017 12:22pm
Okay im going to run the boyesen rad valve now but mybquestion is would the condition of the reed cage cause the mid range sputter/bog?
hawk101
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hawk101 10/12/2021 5:44pm
10/12/2021 5:44pm
I HEREBY REVIVE THIS THREAD!!!!

I've got the sample problem as you and even replaced the CDI. Still the midrange sputter/bog. My jetting was perfect before.

Did you ever solve your bike problem?

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